<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>$课堂练习$</title>
</head>
<body>
<script>
    var sum = 0;
    for (var i = 0; i < 5; i++) {
        sum += i;
    }
    console.log(sum);
</script>
</body>
</html>